Efficient industrial-current-density acetylene to polymer-grade ethylene via hydrogen-localization transfer over fluorine-modified copper

Electrocatalytic acetylene semi-hydrogenation to ethylene powered by renewable electricity represents a sustainable pathway, but the inadequate current density and single-pass yield greatly impedes the production efficiency and industrial application. Herein, we develop a F-modified Cu catalyst that shows an industrial partial current density up to 0.76 A cm−2 with an ethylene Faradic efficiency surpass 90%, and the maximum single-pass yield reaches a notable 78.5%. Furthermore, the Cu-F showcase the capability to directly convert acetylene into polymer-grade ethylene in a tandem flow cell, almost no acetylene residual in the production. Combined characterizations and calculations reveal that the Cuδ+ (near fluorine) enhances the water dissociation, and the generated active hydrogen are immediately transferred to Cu0 (away from fluorine) and react with the locally adsorbed acetylene. Therefore, the hydrogen evolution reaction is surpassed and the overall acetylene semi-hydrogenation performance is boosted. Our findings provide new opportunity towards rational design of catalysts for large-scale electrosynthesis of ethylene and other important industrial raw.


Supplementary Figures and Tables
Figure S1.Digital paragraph of Cu(OH)F, which takes an appearance of light-green slice and powder.

Figure S2 .
Figure S2.SEM image of Cu(OH)F.The as-prepared Cu(OH)F exhibits a morphology of the accumulation of nanosheets.

Figure S4 .
Figure S4.TEM images of Cu-F.The Cu-F reveals the aggregation of irregular nanoparticles with a size ranging from 45-90 nm, and the lattice spacing are measured at 0.208 nm that corresponding to the Cu (111) plane.

Figure S5 .
Figure S5.F 1s XPS spectra of Cu-F and Cu(OH)F.The Cu (OH)F and Cu-F shows similar binding energy for F 1s, indicating the adsorbed F in Cu-F.

Figure S6 .
Figure S6.The LSV curve of the Cu(OH)F reduction recorded in 1 M KOH with a Ar flow (30 ml min -1 ) and a scan rate of 10 mV s -1 .

Figure S7 .
Figure S7.Cu 2p XPS spectra of Cu-F.Cu-F exhibits a binding energy for Cu 2p3/2 at 932.7 eV, slightly higher than the 932.4 eV for Cu 0 .

Figure S8 .
Figure S8.LMM spectra of Cu-F, which indicates the co-existence of Cu 0+ and Cu + in Cu-F

Figure S10 .
Figure S10.Wavelet transformations of CuO, Cu(OH)F and Cu foil.This observation in agreement with the FT EXAFS spectra in Figure 1g, indicating the partial coordination of Cu with F in the Cu-F catalyst.

Figure S15 .
Figure S15.Digital graph of the 1 cm 2 flow cell, which is mainly consisted by cathode liquid chamber, anode liquid chamber, feed gas chamber and support plate.

Figure S17 .
Figure S17.ECSA-normalized electrocatalytic performance of various catalysts.(a) LSV curves of HER measured under Ar flow.(b) C2H4 formation rate at -1.0 V measured under 70 mol% C2H2/Ar flow.Measured using a three-electrode flow cell (1 cm 2 ) in 1 M KOH at room temperature with gas flow rate of 30 ml min -1 .The results are presented without iR compensation.

Figure S18 .
Figure S18.ESAE performance of Cu-F at different flow rate of the feed gas.(a) Single-path C2H2 conversion vs. current density, the maximum measurement error is ± 4.6%.(b) LSV curves.Measured using a three-electrode flow cell (1 cm 2 ) in 1 M KOH at room temperature under 70 mol% C2H2/Ar flow.The results are presented without iR compensation.

Figure S19 .
Figure S19.Gas chromatography analysis of the outlet gas from flow-cell.Ethylene (C2H4) is identified as the main production, accompanied by few H2 and C4.

Figure S20 .
Figure S20.Liquid NMR analysis of the electrolyte after the ESAE evaluation in flowcell.Acetone origins from C2H2 feed gas.No liquid production is detected in the used electrolyte.

Figure S22 .
Figure S22.Faradaic efficiency of the ESAE productions vs. applied potential over Cu-F in neutral and acidic medium.Measured using a three-electrode flow cell (1 cm 2 ) in 0.5 M K2SO4 or H2SO4 at room temperature under 70 mol% C2H2/Ar flow (30 ml min - 1 ).The results are presented without iR compensation.

Figure S24 .
Figure S24.Faradaic efficiency of the ESAE productions vs. applied potential over Cu-Cl.Measured using a three-electrode flow cell (1 cm 2 ) in 1 M KOH at room temperature under 70 mol% C2H2/Ar flow (30 ml min -1 ).The results are presented without iR compensation.The maximum measurement error is ±3.4%.

Figure S25 .
Figure S25.Faradaic efficiency of the ESAE productions vs. applied potential over Cu-Br.Measured using a three-electrode flow cell (1 cm 2 ) in 1 M KOH at room temperature under 70 mol% C2H2/Ar flow (30 ml min -1 ).The results are presented without iR compensation.The maximum measurement error is

Figure S27 .
Figure S27.C2H2 conversion and C2H4 selectivity of Cu-F vs. reaction time in the longterm stability test.Faradaic efficiency of the ESAE productions vs. applied potential over Cu NP.Measured using a three-electrode flow cell (1 cm 2 ) in 1 M KOH at room temperature under 70 mol% C2H2/Ar flow (30 ml min -1 ).A constant current density is set at 200 mA cm -2 .

Figure S29 .
Figure S29.The effect of the leached F in the electrolyte.(a) LSV curves.The orange sphere represents the curve measured in the original electrolyte used for generating Cu-F, which may contain the leached F -; The bule line represents the electrolyte is replaced by a fresh one after the generation of Cu-F.(b) FE and the current density, the maximum measurement error is ±2.8%.

Figure S30 .
Figure S30.The in-situ XAFS measured on the generation process of Cu-F and the subsequent acetylene semi-hydrogenation process.(a) The Cu k-edge XANES spectra.(b) Cu k-edge FT-EXAFS spectra.Measured at -0.6 V vs. RHE (-1.6 V vs. Ag/AgCl) in different feed gas at different time.

Figure S31 .
Figure S31.The operando Raman device used in this work.A three-electrode observable window electrochemical cell with a counter electrode of carbon rod and Ag/AgCl under controlled potentials in 1 M KOH electrolyte, and a controlled active area by an insulation layer on carbon paper sprayed with 1 mg Cu(OH)F was used as the working electrode.

Figure S32 .
Figure S32.The LSV curves of Cu-F in KOH solution with different concentration.Measured using a three-electrode flow cell (1 cm 2 ) at room temperature under 70 mol% C2H2/Ar flow (30 ml min -1 ).The results are presented without iR compensation.

Figure S33 .
Figure S33.The effect of the KOH concentration on the FE over Cu-F.Measured using a three-electrode flow cell (1 cm 2 ) at room temperature under 70 mol% C2H2/Ar flow (30 ml min -1 ).The results are presented without iR compensation.

Figure S34 .
Figure S34.The effect of the KOH concentration on the C2H4 formation rate over Cu-F.Measured using a three-electrode flow cell (1 cm 2 ) at room temperature under 70 mol% C2H2/Ar flow (30 ml min -1 ).The results are presented without iR compensation.

Figure S35 .
Figure S35.(a) Potential-dependent C2H2 conversion change over Cu-F with or without the addition of tert-Butanol in the electrolyte, the maximum measurement error is ± 4.8%.(b) FE of Cu-F with tert-Butanol in the electrolyte.Measured using a threeelectrode flow cell (1 cm 2 ) in 1 M KOH at room temperature under 70 mol% C2H2/Ar flow (30 ml min -1 ).The results are presented without iR compensation.

Figure S36 .
Figure S36.The KIE of Cu-F, Cu-Cl, Cu-Br, Cu-I and Cu NP.Measured using a threeelectrode flow cell (1 cm 2 ) in 1 M KOH (H2O and D2O as solvent respectively) at room temperature under 70 mol% C2H2/Ar flow (30 ml min -1 ).The results are presented without iR compensation.The maximum measurement error is ±4.9%.

Figure S37 .
Figure S37.LSV curves in pure Ar over Cu-F with 1 M KOH, NaOH and TMAH electrolyte.Measured using a three-electrode flow cell (1 cm 2 ) at room temperature under Ar flow (30 ml min -1 ).The results are presented without iR compensation.

Figure S38 .
Figure S38.(a) C2H2 conversion measured under 70 % C2H2/Ar (30 ml min -1 ) flow and (b) LSV measured under pure Ar flow (30 ml min -1 ) over Cu NP in 1 M KOH, NaOH and TMAH electrolyte.Measured using a three-electrode flow cell (1 cm 2 ) at room temperature The results are presented without iR compensation.The maximum measurement error is ±3.6%.

Figure S39 .
Figure S39.The simulative structure of the Cu sites near and far from the F atom in Cu-F.

Figure S40 .
Figure S40.The simulative structure of the Cu (111), which displays the (111) plane of crystalline Cu, matching the physical characterizations of Cu-F.

Figure S41 .
Figure S41.Energy of the system as function of the transfer pathway for a surface *H on Cu-F, calculating based on CINEB.

Figure S42 .
Figure S42.Free energy diagram for the hydrogenation of C2H2 at -1.0 V vs. RHE, which displays the similar trend with that at 0 V vs. RHE, but the reaction barrier is reduced.

Figure S43 .
Figure S43.Free energy diagram for the hydrogen combination at 0 V vs. RHE.The H2 generation barrier of Cu (111)-F-far is measured as 0.29 eV, higher than the C2H2 semi-hydronation barrier of 0.12 eV.

Figure S44 .
Figure S44.ESAE performance of Cu-F under C2H2/Ar flow with different C2H2 concentration (mol%, 30 ml min -1 ).(a) LSV curves.(b) Faraday efficiency and current density at different C2H2 concentration.Measured using a three-electrode flow cell (1 cm 2 ) in 1 M KOH at room temperature.The results are presented without iR compensation.

Figure S45 .
Figure S45.Digital image of the 25 cm 2 flow-cell with S type gas chamber, which is mainly consisted by cathode liquid chamber, support plate, anode liquid chamber and S-type gas chamber.

Figure S46 .
Figure S46.Selectivity vs. time of Cu-F in a 25 cm 2 flow-cell.Measured using a threeelectrode flow cell (25 cm 2 ) in 1 M KOH at room temperature under 1 mol% C2H2/C2H4 flow (20 ml min -1 ).A constant current density is set as 40 mA cm -2 .The results are presented without iR compensation.

Figure S47 .
Figure S47.(a) Chromatogram and (b) the corresponding standard curve of C2H2 with different volume fractions for the quantitation of C2H2 conversion.

Figure S48 .
Figure S48.The tandem device composed of a 1 cm 2 and a 25 cm 2 flow-cell.The designing is based on the capacity of the 1 cm 2 flow cell to deal with high concentration C2H2 feed gas, and the ability of the 25 cm 2 flow cell for converting residual C2H2 at low concentration.

Figure S49 .
Figure S49.C2H4 selectivity vs. current density at different flow rate.Measured using a three-electrode flow cell (1 cm 2 ) in 1 M KOH at room temperature under 70 mol% C2H2/Ar flow.The results are presented without iR compensation.The maximum measurement error is ±4.7%.

Figure S50 .
Figure S50.The carbon distribution in the outlet gas of the tandem device, which indicates a negligible carbon loss.

Table S1 .
Element contents in the halogen-containing copper catalyst measured by XPS.

Table S2 .
Capacitance, surface roughness factors and electrochemical surface areas (ECSA) for Cu-X(F, Cl, Br, I) and Cu NP a Cs the corresponding smooth polycrystalline Cu electrode.

Table S3 .
The comparison of acetylene semi-hydrogenation performance via electro-

Table S4 .
The Ru resistances measured at working conditions in electrode system.